Topic 32 - Properties of circulation in the coronaries, the skin, the brain, splanchnic circulation, and the fetal circulation

Question 1

Words to include in circulation in the coronaries

Answer 1

• A. coronaria dextra
  
  • Right atrium
  • Right ventricle
• A. cornaria sinistra
  
  • Left anterior descending arterie
    
    • A. descendens
      
      • Anterior septum
      • Anterior left ventricular wall
  • Left circumflex arterie
    
    • A. circumflexus
      
      • Left atrium
      • Left ventricle
• Conductive system
  
  • Bradycardia
  • Stenosis (in a. coronaria sinistra)
• Beginning of systole (isovolumetric contraction)
  
  • Reverse blood flow
• Fast ejection phase
  
  • Aorta pressure high
• Slow ejection phase
  
  • Aorta pressure drops
  • Coronary perfusion (↓)
• Diastole
  
  • Maximum coronary flow
• Aortic pressure (mmHg)
• Coronary flow (ml/min/100g)
• Isovolumetric contraction
• Ejection

Question 2

Words to include in circulation in the brain

Answer 2

• Venous blood flow
• Arterial blood flow
• Overpressure
• Hypoxia
  
  • Local reflex mechanisms
• Cushing-effect
  
  • Intracranial pressure (↑)
  • Peripheral blood pressure (↑)
  • Compressed vasomotor center
• pCO₂
• pH
• N. facialis
  
  • Parasympathetic innervation
• 60-160 mmHg
  
  • Edema (over)
  • Syncope (under)
• Myogenic tone
• Intravasal / EC volume ratio
• Circle of Willis
• Closed cerebral cavity

Question 3

Words to include in circulation in the skin

Answer 3

• Metabolic demand
• Thermoregulation
  
  • Heat balance regulation
    
    • Vasoconstrictor tone
    • A-V anastomoses
• Skin capillaries
• Arterioles
• Vessel reflexes

Question 4

Words to include in splanchnic circulation

Answer 4

• Double capillary system
  
  • Two serially attached capillary systems
    
    • Portal circulation
• Myogenic tone (ø)
• Sympathetic tone
  
  • α-receptor
• Metabolic autoregulation (less developed)
• Splanchnic area
  
  • Liver
    
    • Reservoir
      
      • 15%

Question 5

Words to include in fetal circulation

Answer 5

• Oxygenated blood
  
  • V. umbilicalis
  • Ductus venosus
• Deoxygenated blood
  
  • A. umbilicalis
• Forame ovale
  
  • Intracardial change
  • Parallelly coupled system
  • Fossa ovalis
• Ductus arteriosus
  
  • Botalis ductus
    
    • Pulmonary circulation
  • Lig. arteriosus
• Ductus venosus
  
  • Arantius duct
• A. umbilicalis
  
  • Lig. teres hepatis
  • 5 mmHg (higher than aorta)
• V. umbilicalis
  
  • Lig. teres hepatis
• V. cava caudalis
  
  • Right atrium (enter)
• Aorta
  
  • Fetal tissue
• Fetal liver
• Right ventricle
• Systemic circulation
• Placenta
• Pulmonary resistance ↓
• Surfacant factors
• Lung
• Prostaglandin liberation

Question 6

Circulation in the coronaries

Answer 6

• The coronary arteries arise from the aorta; they are separated into the left and the right coronary arteries
• A. Coronaria dextra: supply the right atrium and ventricle, continues down and supply also the posterior left ventricular wall and the posterior part of the interventricular septum
  
  • Known as the posterior descending coronary artery
• A. Coronaria sinistra: divide into left anterior descending and left circumflex arteries
  
  • A. Descendens: supplies the anterior septum and the anterior left ventricular wall
  • A. Circumflexus: supplies left atrium and ventricle
• The conductive system is also supplied by the coronary arteries
• Disease of the coronary arteries may cause:
  
  • Bradycardia
  • Stenosisof thea. coronaria sinistra

1. Beginning of systole (isovolumetric contraction)
   
   • The tension of the left chamber of the heart is so high that the blood will be pressed out from the coronary vessels, then reversed blood flow will occur
   • Reverse flow will not occur in the right chamber, but it will have the same effect except from that
2. Fast ejection phase
   
   • The high pressure in the aorta secures the flow in the coronary arteries
3. Slow ejection phase
   
   • The pressure in the aorta drops
   • Therefore the coronary perfusion slows down
4. Diastole
   
   • More blood enter the coronary vessels (more than during systole), maximum coronary flow can be measured

Question 7

Circulation of the brain

Answer 7

• Venous and arterial blood flow to and from the brain is equal; if not the brain tissue could suffer from overpressure
• The brain tissue is very sensitive to hypoxia; therefore there are local reflex mechanisms that keep the blood flow constant
• Cushing-effect: when the intracranial pressure increases, then the peripheral blood pressure increases as well to keep the constant blood flow to the brain
  
  • Most likely caused by hypoxia in the compressed vasomotor center
• Blood flow in the brain can be altered by:
  
  • pCO₂
  • pH
    
    • ↓ pH = ↑ blood flow
• N. Facialis: parasympathetic innervations of the brain vessels
• The brain can tolerate a change in the mean blood pressure between 60 – 160mmHg
  
  • Over: edema
  • Under: syncope (fainting, collapse)
• Myogenic tone

Question 8

Circulation of skin

Answer 8

• Low metabolic demand
• Crucial area of thermoregulation / heat balance regulation
• Flow rate varies in a very large range
• Vasoconstrictor tone is of major importance
• A-V anastomoses
• Arterioles regulate
• Vessel reflexes of the skin is of diagnostic importance

Question 9

Splanchnic Circulation

Answer 9

• Two serially attached capillary systems: portal circulation
• Myogenic tone is almost non existent
• The main regulator is the sympathetic tone (α-receptor)
• Metabolic autoregulation is less developed
• In the liver (a. Hepatica), myogenic autoregulation occurs
• The splanchnic area (liver) serves as a reservoir
  
  • 15% of the circulating blood volume resides here in resting conditions

Question 10

Fetal circulation

Answer 10

• The fetus receives the oxygenated blood through the v. Umbilicalis
  
  • This blood is saturated with oxygen by 85%
• Most of the blood reaches the fetal liver, while a small part of it reaches the heart directly through the v. cava caudalis
• Finally blood goes from the liver → right ventricle
• Left and right atria communicate with each other through the foramen ovale
• In the fetus the left and right ventricles work as a parallelly coupled system, as most of the blood pumped out from the right ventricle circumvents the resistant lung tissue
• Blood goes through the ductus arteriosus → aorta and is then added to the systemic circulation
  
  • Pressure in the a. pulmonalis is approximately 5 mmHg higher that in the aorta
• Blood from aorta:
  
  • One third goes to the cranial part of the body
  • Rest is delivered to the caudal one
    
    • Half of this blood goes through the placenta
• After delivery:
  
  • Sudden increase of the pulmonary circulation sets in
  • The pulmonary resistance decreases
    
    • Because of the surfactant factors after the onset of breathing
  • More and more blood goes through the lung
  • Pressure decreases in the right atrium as compared to the left atrium
    
    • Leads to the closure of the foramen ovale = fossa ovale
    • Pressure decreases in both the a. pulmonaris and ductus arteriosus
  • Pressure drop → prostaglandin liberation
    
    • Closes the ductus arteriosus = lig. arteriosum
• Muscles of the left ventricle develop rapidly and finally the serially coupled pulmonary and systemic circulation evolves
• Comparison of fetal and adult circulation:
  
  • For. ovale = Fossa ovale
  • Ductus arteriosus (Botalli) = Lig. arteriosum
  • A/V. umbilicalis = Lig. teres hepatis